The present invention relates generally to applicators that are used to spray fluids, such as paint, sealants, coatings, enamels, adhesives, powders and the like. More particularly, the invention relates to electrostatic spray guns.
In electrostatic spray systems, an electrostatic field is produced in the vicinity between the spray gun and the target or article to be sprayed. The sprayed particles are propagated through this field, and the respective particles pick up electrical charges as they pass through the field. The charged particles are thereby attracted to the article to be sprayed. By this process, it is possible to direct a much higher percentage of sprayed particles to the actual article to be sprayed, and thereby the efficiency of spraying is vastly improved over conventional methods. Electrostatic spray guns are particularly useful for applying non-conductive liquids and powders, although they may be used in connection with spraying conductive liquids.
In a typical electrostatic spraying system, an ionizing electrode is placed in the vicinity of the spray gun spray orifice, the article to be painted is held at ground potential, and an electrostatic field is developed between the ionizing electrode and the article. The distance between the electrode and ground may be on the order of about 0.5 meters or less; therefore, the voltage applied to the spray gun electrode must necessarily be quite high in order to develop an electrostatic field of sufficient intensity to create a large number of ion/particle interactions so as to develop a sufficient attractive force between the paint particles and the target. It is not unusual to apply electrostatic voltages on the order of 20,000-100,000 volts (20-100 kV) to the spray gun electrode in order to achieve a proper degree of efficiency in the spraying operation. An ionizing current on the order of 50 micro-amps typically flows from the spray gun electrode.
Electrostatic spray guns may be hand-held spray guns or automatic spray guns operable by remote control connections. The sprayed fluid may be atomized using different primary atomizing forces, such as pressurized air, hydraulic forces, or centrifugal forces. Power for the electrostatic voltage may be generated in a variety of ways. In many systems, an external power source is connected to the electrostatic spray gun. However, in other designs, power may be generated with an alternator located in the electrostatic spray gun. For example, U.S. Pat. Nos. 4,554,622, 4,462,061, 4,290,091, 4,377,838, 4,491,276 and 7,226,004 describe electrostatic spray guns having an air-powered turbine which drives an alternator that in turn supplies a voltage multiplier to provide the charging voltage.